Chap. 9] 



SEISMIC METHODS 



517 



If the same profile is shot in the opposite direction, a travel-time curve 

 identical with the one for a single horizontal layer, but with increased 

 intercept distance, is obtained (Fig. 9-53). Hence, its interpretation 

 alone would give too great a depth unless the same profile is shot in the 

 opposite direction. Together, both travel-time curves furnish an accurate 



Fig. 9-54. Travel-time curve, Marafael, Venezuela (adapted from O. v. Schmidt), 

 value for the location of the vertical face. If, from the up-scarp time 



'• = - 



Vi cos X V2 



the U. down-scarp time for the same distance. 



B — e — d tan % . y/e^ -^ d^ 



H ~ n z > 



Vi 



fe = 



2d s - 2d tan i 



V2 



Vi cos I 

 is deducted, one obtains for e 



Vi(f3 — ti) -\- d cos i 



e = 



/-©■- 



(9-48c) 



sm t 



where e' is the approximate distance of the scarp from the shot point calcu- 

 lated from eq. (9-486). 



